In an effort to identify cell surface molecular sites mediating intercellular adhesions, lectins that agglutinate the cells are being degraded to produce non-agglutinating blocking agents specific for particular cell surface saccharide sites. These lectin fragments are being characterized biochemically. The consequences of blocking specific cell surface saccharide sites are determined through assays of cell aggregation and cell sorting. The parent lectins of non-agglutinating lectins that inhibit cell adhesion are then being immobilized on affinity columns and used to extract the corresponding cell surface glycosubstances from solution. These substances are then to be examined for their own effects on the adhesion of homologous and heterologous cells. In order to make possible the routine measurement of the intensities of intercellular adhesion within cell aggregates (aggregate sigma's), a new, rapid and relatively simple technique, the aggregate-oil drop fusion technique, has been conceived and partially developed. We propose to complete the development of this method and to apply it to test two important hypotheses: (1) that malignant invasive and metastatic behavior results from too-low intercellular adhesiveness, and (2) that certain morphogenetic tissue rearrangements result from particular kinds of intercellular adhesive differentials.